Sunday, January 29, 2012

Oxidation in Beers

I'll admit I had a flavor problem that I had a difficult time tracing, and it ended up being oxidation. This article will describe how I arrived at the conclusion that oxygen was to blame, and also how I addressed the issue.

The curious thing about the off-flavor was that my beer tasted perfect when primary fermentation was done, when I transferred to secondary, when I transferred to the keg, and probably 2-3 weeks after that. However, as the beer aged, it took on tastes similar to sherry or cough syrup...regardless of the style of beer.

John Palmer writes about off-flavors in his How To Brew publication (see section 21.2), and this helped confirm the flavor. Additionally, a couple friends offered advice on how to diagnose and address it. I'll admit I was somewhat lax when it came to preventing oxidation, so I took the following steps:

When I transfer beer to the secondary, I purge the secondary vessel with CO2, and siphon slowly, all while flowing CO2 gently.

When transferring to the keg, I follow the same procedure: flowing CO2 into the keg during transfer.

It doesn't hurt to make a few other changes that were probably overdue, or just good practice, so I also did these:

Replaced all beverage and siphon tubing.

Ran PBW through by counterflow chiller multiple times, and let it sit for a while, too.

Ferment in glass (I will be avoiding white food grade plastic, as it is not impermeable to oxygen, and also can take on flavors).

Use only the refractometer Santa gave me from now on.

Watch my sparge temperatures more carefully.

So far, the chocolate coffee oatmeal stout I made has passed the 4 week mark, so I'm pretty confident the problem was either solely oxidation, or oxidation plus old serving/siphon lines. If you notice a sherry-like or cough syrup taste (I never got the cardboard taste many describe), you may have the same issue that plagued a few of my beers. It is a terrible waste to spend all the time, effort, and money on great beer, and have it spoil!